Fix documentation of Timber.Tree.log() params

[vaughandroid]

No description provided.

[vanniktech]

I do not think we need this anymore since this method got the @Nullable and @NotNull annotation and hence this could be closed.

[realdadfish]

@vanniktech Yes, the annotations are now in place, however, that the stacktrace of a throwable - if present - is always attached to the message is still worth documenting IMHO. I don't know what lead to this decision, as it kind of makes giving the Throwable as argument superfluous (and impossible to easily separate the original log message from the exception's trace), but well. I'd have expected - on this level - that if no message was given that just the message, but not the whole stack trace of an exception would have been put into the message.

[tschuchortdev]

@vanniktech It's been 2 years, why has this not been merged yet? Leaving the misleading documentation like this is just bikeshedding.